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Not Applicable.
1. Field of the Invention
The present invention relates in general to electronically-controlled fuel vapor management valves, and in particular to an electronically-controlled proportional solenoid valve for purging fuel vapors.
2. Description of the Related Art
Modern vehicles are equipped with emission control systems designed to limit the emission of hydrocarbons into the atmosphere. These emission control systems typically use an evaporative emission control design to trap fuel vapors from the fuel tank in a canister, which is usually carbon filled, and a purge system designed to draw the vapors from the canister into the engine intake manifold for combustion.
Conventional evaporative emission control systems are equipped with a fixed area purge valve for regulating the flow rate of fuel vapors introduced into the intake system in response to the pressure difference between the intake manifold and atmosphere. These purge valves typically utilize a pulse width modulated (PWM) solenoid valve which is responsive to a duty cycle control signal from an engine controller unit (ECU) which is usually microprocessor based, for selectively establishing and terminating communication between the canister and the intake system. These purge valves often provide uneven flow characteristics, particularly at low engine speeds, and also do not provide consistent flow control independent of variations in manifold vacuum and inlet pressure.
A recent design in U.S. Pat. No. 5,277,167, which is commonly owned by the Assignee of the present invention and hereby incorporated by reference, discloses a vapor management valve that combines an electric vacuum regulator (EVR) valve with a vacuum regulator valve. That device generates an output flow characteristic that is proportional to the duty cycle of the electric control signal independent of variations in the manifold vacuum.
U.S. Pat. Nos. 5,551,406 and 5,727,532 both relate to on-board evaporative emission control systems, and disclose still other designs of the cannister purge valve.
In order to satisfy even more increasing stringent emission regulations from the Environmental Protection Agency (EPA), it is necessary to provide purge flow even at engine idle speeds. The purge flow control must also be accurately regulated across the entire engine operating range so as not to cause unacceptable exhaust emissions. U.S. Pat. No. 5,970,958 discloses a fuel vapor purge control system with a variable area valve and pressure regulator. This device is operable to generate non-linear output flow characteristics independent of changes in the intake manifold vacuum. This patent is also assigned to the Assignee of the present invention and hereby incorporated by reference.
There still exists a need for an improved linear proportional solenoid valve which enables better proportional flow control and has increased durability. It is desirable to have a linear proportional solenoid valve with low friction. The low friction enables better proportional flow control of the fuel vapors with the appropriate driver circuit. Additionally, it is desirable that the linear proportional solenoid valve have increased durability. This allows the linear proportional valve to be mounted horizontally which would make the valve less sensitive to road and/or engine vibrations.
One object of the present invention is directed to overcoming the aforementioned problems by providing an improved proportional solenoid valve for purging fuel vapors constructed to meet tougher emission standards for vehicles, including but not limited to, both passenger cars and light duty trucks.
Another object of the present invention is to provide an improved linear proportional solenoid valve for controlling the purging of fuel vapors collected in a canister of an evaporative emission control system.
Still another object of the present invention is to provide an improved linear proportional solenoid valve for purging fuel vapors that includes a design which enables the valve to have extremely low friction.
Still another object of the present invention is to provide a linear proportional solenoid valve assembly that includes a spider spring feature for absorbing most of the magnetic and gravitational side floating.
Still another object of the present invention is to provide a linear proportional solenoid valve with increased durability to allow the valve to be mounted horizontally making it less sensitive to road and/or engine vibrations.
Still another object of the present invention is to provide a linear proportional solenoid valve for controlling the flow of fluid from a fluid source to a fluid sink.
Still another object of the present invention is to provide a method for purging fuel vapors of an internal combustion engine.
Still another object of the present invention is to provide a linear proportional solenoid valve assembly which is rugged in construction and economical to manufacture.
The linear proportional solenoid valve in accordance with the present invention comprises a housing having a chamber formed therein, an inlet port providing fluid communication from a canister to the chamber, and an outlet port providing fluid communication from the chamber to an intake system of an internal combustion engine, and a solenoid valve assembly which includes an armature, an electromagnetic coil, and a valve member operatively connected to the armature and disposed between the inlet port and the outlet port for controlling fluid flow therethrough in accordance with an electrical control signal supplied to the electromagnetic coil. Advantageously, in accordance with the present invention, the armature is disposed outside of the electromagnetic coil of the solenoid valve assembly and includes means for resiliently biasing the armature away from the electromagnetic coil. The linear proportional solenoid valve in accordance with the preferred embodiment of the present invention employs a spider spring separating the armature from the valve member. The spider spring is constructed to absorb most of the magnetic and gravitational side load from the armature.
The present invention is also directed to a method for purging fuel vapors of an internal combustion engine which comprises the steps of collecting fuel vapors in a canister, providing a housing with a chamber formed therein, an inlet port for fluidly communicating from the canister to the chamber, and an outlet port for fluidly communicating from the chamber to an intake system of the internal combustion engine, disposing an electrically operated valve assembly with a valve member in the housing with a valve member being positioned between the inlet port and the outlet port, the electrically operated valve assembly having an armature and an electromagnetic coil operative to control movement of the armature, disposing the armature in a biased position outside of the electromagnetic coil of the electrically operated valve assembly and opening the valve member periodically with a valve shaft responsive to movement of the armature at periodic intervals for purging fuel vapors from the canister for combustion in the internal combustion engine.
The various features of novelty which characterize the present invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.